This invention pertains to the art of continuous casting and more particularly to the inductive heating of endless flexible casting belts of a continuous caster.
The invention is particularly applicable to inductive heaters used to preheat the endless belts of a continuous caster which casts molten metal and will be described with particular reference thereto. However, it will be appreciated that the invention has broader applications and may be advantageously employed in other environments and applications.
In a device for continuously casting molten metal, it is known that at least two endless flexible belts constructed of a durable material, such as carbon steel, are mounted on sets of pulleys such that the front surface of the two belts are in a facing relationship. It is further known that a pair of dam blocks can be located at the outer edges of at least one of the endless belts front surfaces. The dam blocks and the endless belts are arranged to form a casting region. Molten metal is delivered into the casting region such that the molten metal is cast into metal of varying width and gauge depending upon dimensions of the casting region. The casting region consists of a casting zone where metal is received in a molten form, and a cooling zone where the metal is caused to solidify.
Additionally, it is further known that the introduction of heat to the endless flexible casting belts causes the belts to expand across their width. When this heating of the belts occurs due to the belts coming into contact with the molten metal, the temperature that is applied to the belts is unregulated and uneven. This unregulated application of heat causes the belts to expand in an uneven nonregulated manner and results in distortions of the metal being cast. In order to eliminate the undesirable effects of this unregulated heating, methods of transferring heat to the belts prior to the belts entering the casting region have been developed. This preheating of the belts will produce a more uniformed casting of the metal by the elimination of belt distortion.
Various types of continuous casting devices and methods employing preheating of belts have been suggested and employed in the continuous casting industry, with varying degrees of success. For example, Hazelett et al. U.S. Pat. No. 3,937,270 employs infra red heaters directed at close range towards the casting surfaces of the belts. This reference also employs heating by means of hot fluid, such as steam, with the hot fluid being directed into deep grooves in the nip roll or pulleys beneath rear surfaces of the casting belts. These methods are applied to twin belt casting machines whether the molten metal is applied by open pool, closed pool or injection feeding.
Steam has also been employed in Hazelett, et al. U.S. Pat. No. 537,243 and UK patent application GB 2,085,779 A to preheat the endless casting belts. These references disclose casting machines which include an apparatus for preheating the casting belt with steam closely ahead of the entrance to the casting zone by providing wrap around steam feed tubes having steam outlet nozzles. These tubes are positioned in very deep circumferential groves in the input pulley or nip pulley which move the casting belt into the input end of the casting zone. These circumferential groves of the input or nip pulley also house wrap around liquid coolant feed tubes for cooling the casting belt in the cooling zone.
However, when using the known apparatuses and methods of preheating the casting belts in a continuous caster, various problems exist. Initially, in order for the preheating of belts to be effective certain temperatures need to be obtained. When using the steam method various practical concerns limit the temperature to which the steam can be raised. In existing casting systems, this temperature has been in the range of 180.degree. to 200.degree. F. Thus for certain metals which require the belts to be preheated to higher temperatures, steam is not a practical solution.
When using infra red to preheat the belts to the required temperature the belts need to be preheated over extended areas of the belts surfaces for considerable periods of times. Therefore, the heating units required to heat the belts to the desirable levels take up considerable physical space within the casting machine. Since the casting machine is a very compact device, especially at the location of the input of the molten metal, the requirements for the significant volume of infra red heaters cause engineering and construction problems in order to provide available space.
Additionally, both with the steam and the infra red heaters an inconsistency in the transfer of heat to the belts exist. For instance, when employing an infra red heating system individual heating units are employed thus decreasing the certainty that a controlled transfer of heat to the belts is occurring. At the same time, if a flame infra red heating device is used, imprecise fuel flow rates can cause flames to issue from the burner housing and burn the endless belts damaging their surface.
The present invention contemplates a new and improved apparatus and method which overcomes all of the above referred to problems and others. The device provides a new continuous casting device with a heating system for preheating flexible endless casting belts which is simple in design, limited in the physical space required to implement it, economical to manufacturer, adaptable to a plurality of dimensional characteristics, is rugged and reliable in its operation, and which provides an improved uniform transference of heat in a substantially instantaneous manner over a limited physical area such that uniform expansion occurs which in turn results in a better uniformed casting of metal.